1. Technical Field
This invention relates generally to material testing and more particularly to nondestructive detection of flaws in objects. A flaw may be a crack in an object, a void in an object and/or a deviation from dimensional specifications of the object, and any other parameter that causes a change in mechanical resonance.
2. Description of the Related Art
FIG. 1 shows an example of an ultrasonic signal (A-Scan) used to detect a defect within a single layered object. The time window 101 is typically determined by the thickness of the object, so that backwall echo 105 is excluded from the ultrasonic scan. FIG. 1 shows an ultrasonic signal in A-scan mode and presents a typical defect echo 110 within the time window 101.
In the case of objects with layers comprising of different ultrasonic impedances for the ultrasonic signal path, this simple detection scheme cannot be used, because at no time is a window present where the signal is zero. This makes it extremely difficult, time consuming and cost prohibitive to detect a defect echo with confidence.
FIG. 2 shows a typical experimental ultrasonic echo signal (A-Scan) obtained from a 3-layered object, where each layer has a different impedance and wherein the object is without defect. This signal, when compared to the signal in FIG. 1, is considered a complex signal. If a defect was present, the signal would be hardly distinguishable from the signal in FIG. 2, which is without defect.
Traditionally, this type of multi-layered object is ultrasonically tested in transmission configuration. In the transmission configuration, the ultrasound generator is placed on one side of the part and the ultrasound detector is placed on the other side. Defects are detected by a significant decrease in the transmitted ultrasonic signal. However, in many cases, the inspection can only be performed from a single side and the transmission technique cannot be used.
FIG. 2A shows a typical experimental ultrasonic signal (B-Scan) obtained from a 3-layered object wherein one lone defect is present.
The invention presents a flaw detection apparatus for detecting flaws within a multi-layered object comprising an object wherein the ultrasonic impedance varies across the ultrasonic signal path of the object and such variance is not due to a defect, a means for collecting an actual signal from an ultrasonic test conducted on the object, a reference signal for the object, a means for comparing the actual signal to the reference signal, and a display means for displaying the comparison signal.
Additionally, the invention presents a method to detect flaws within a object comprising the steps of producing an actual ultrasonic test signal for the object, comparing the actual signal to a reference signal for the object, and displaying the compared results.
Additionally, the invention presents an apparatus for performing ultrasonic testing of an object, the apparatus comprising a means for receiving an actual ultrasonic signal from the object, a means for comparing the actual signal to a reference signal for the object and a means for displaying the comparison result.
The foregoing has outlined some of the more pertinent objects and features of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the invention. Applying the disclosed invention in a different manner can attain many other beneficial results or modifying the invention as will be described. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the following Detailed Description of the Preferred Embodiment.